Receiver



- alloy Patented Sept. 20, 1927.

UNITED STATES PATENT OFFICE.

, eus'rnr w. ELMEN,

OF LEONIA, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

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Application filed. November 4, 1924. Serial No. 747,718.

This invention relates to receivers, and more particularly, to a diaphragm for use in the magnetic circuit of a telephone receiver.

In my copending application Serial No. 492,722, filed August 16, 1921, I have described an electromagnetic device such as a telephone receiver in which at least a portion of the magnetic .circuit is composed of a material having veryhigh permeability at low magnetizing forces.

For certain uses I have stated that an containing approximately 78%% nickel and 21%% iron is the most suitable material, but for other uses,this proportion may vary somewhat and in certain cases it may even be desirable to add a third ingredient. In other words, to obtain the best results in a particular case, it is desirable to employ as the magnetic material, an alloy in which. the proportion of the ingredients and the heat treatment provided are such as to give the optimum characteristics for that particular use.

It is the object of the present invention to increase the sensitivity of an electromagnetic device such as a telephone receiver. This object is accomplished by improving the characteristics of the vibrating diaphragm thereof. -In a telephone receiver particularly in one of the electromagnetic type, it is necessary that thereceiver be an eflicient transducer for converting the electrical energy of the speech currents into sound energy and, furthermore, the maximum'efiicienc should be realized under the conditions existing on long subscriber loops where the magnetizing current is a minimum and the flux density in the diaphragm is therefore low.

In a receiver of this type, there are two forces which play an important part in determining its characteristics, namely, a variable force resulting from the combined ac-. tion of the polarizin and the variable flux and a steady force ue to the action of the polarizing flux alone. The former constitutes the useful driving force and ythe latter owing to the control which it exerts over the reluctance of the air gap influences not only the efficiency at small magnetizing currents, but is instrumental in determining the magnetizing current at which maximum efficiency occurs. The magnitude of the steady force resulting from the polarizing flux at high magnetizing currents, also has an important bearing on the stability of the receiver, since it is influential in determining the minimum separation which may be employed between the diaphragm" and pole pieces. On long subscriber loops where the magnetizing current is small and the flux density in the diaphragm is therefore low, the length of the air gap determines the magnitude of the polarizing flux.

Therefore, the effective permeability becomes the most important factor in determining the useful driving force. Since the terminal impedances of the receiver considered as a transducer are fixed by the electrical impedance of the apparatus at the subscribers station and the acoustic impedance of the ear, the number of turns which can be employed in the energizing winding and the mass of the diaphragm are limited. It is necessary, therefore, if the receiver is to be most efficient on long loops and not introduce transition losses of an electrical and mechanical nature that the diaphragm be of low mass and of such a material and thickness that it will approach saturation with the current supplied on long subscriber loops.

In accordance with a feature of the invention a vibrating diaphragm such as a receiver diaphragm is composed of a material which when properly heat treated has a very high effective permeability at low magnetizing forces. Furthermore. the elasticity and other mechanical properties of the material are such as to permit the use of a diaphragm of low mass to meet the requirements of maximum efiiciency at low magnetizing forces.

This and other features ofv the invention will be more clearly understood by reference to the accompanying drawing in which:

Fig. 1 isa sectional view of an electromagnetic receiver embodying the features of this invention.

Fig. 2 is a, view of the diaphragm of Fig. 1. v

Fig. 3 shows the gain in efliciencyresulting from following this invention.

-Fig. 4 contains curves showing the variation in effective permeability at different magnetizing forces or various magnetic materials.

Referring more particularly to Fig. 1 the receiver comprises an energizing winding 5 mounted on the center leg 6 of an E-shaped pole piece comprising the outer legs 7-7.

I This pole piece is rigidly secured as by weldfused together in an induction furnace prefsomewhat from these figures.

erably in the proportion of 55% iron and 45%nickel, good commercial grades of these materials being suitable for this purpose. The molten composition is then poured into a mold and cooled either in theform in which it is later to be em' loyed or in a convenient form to be wor ed over for that purpose. While 55 iron and 45% nickel are mentioned as being the proportion of nickel and iron preferably employed, it should be understood that this proportion may deviate To develop the utmost permeability of this magnetic material, the finished parts are subjected to a heat treatment which in particular cases varys somewhat as regards the temperature employed and the duration of the heating and cooling criods. The optimum values of these varia les may be readily determined for a specific case by experiment. In the case of diaphragms the preferred composition consisting of the 55% iron and nickel is rolled into sheets, approximately.

six thousandths of an inch thick. The-diaphra'gms are then punched from these sheets which may be stretched before the diaphragms are punched therefrom in order to insure perfectly flat diaphragms, or the stretching ma -be omitted and the completed diaphragms attened under pressure. The diaphragms are then placed in a container between suitable blocks of lavite or similar material and are heated to a temperature of. 1,100 centigrade and maintained at this temperature for aperiod of one hour, after which, the are slowly cooled. The temperature to w ich the diaphragms are heated as. well as the period during which they are maintained at the high temperature may vary considerably; A temperature as low as 950 C. has been successfully used.

' Refe'rringto Fig. 3 curve A shows the gain in efiicienc expressed in transmission units or miles 0 standard cable, of an elecpieces of this preferre tromagnetic receiver Q rovided with pole composition, and a ferro-type diaphragm as compared with a standard type of subscribers station re-v ceiver. Curve B show the greater gain in efiiciency resulting from also replacing the ferro-type diaphragm with a diaphragm of the preferred composition. It will be noted that .not only is the maximum efiiciency much higher in the case of the receiver equipped with the nickeliron diaphragm, but this maximum eliioiency is attained a'ta lower magnetizing force corresponding to {he conditions present on long subscriber oops. p

In Fig. 4 curve A shows the variationin A. C. permeability for a. very pure grade of magnetic iron for various superimposed direct current magnetizing forces, and curve B shows the variation in A. C. permeability under similar conditions of an alloy containing 55% iron and 45% nickel when 'ven the preferred heat treatment. It will e noted that for small magnetizing forces of the or- Y from .a sheet of magnetic material, eating said diaphragm to a tem erature of the order of 1000 C. and slow y cooling it.

2. A diaphragm composed-of nickel and iron heat treated .to develop its maximum permeability.

3. A vibrating diaphragm composed of 5 approximately 55%iron and 45% nickel.

4. In a. telephone receiver, ama etic circuit in'which the pole pieces and laphragm are composed of a nickel-iron allo having] low magnetizing tion' oint.

6.- n a; telephone receiver, a ma orces and a lower saturaetic' circuit-in which the pole pieces and iaphragmv are composed of a magnetic'materlal con i taining approximately 55% iron and 45% nickel.

a permeability hi her than that 0 iron for.

are composed of a. nic el-iron alloy having a permeability higher than that of iron at- 7. A. vibrating diaphragm havingan alter nating current permeability higher than that v direct current magnetizing force. g

' 8.A vibrating diaphragm composed of of iron when'subjected to asuperimposed material having a higher effective permevariable 'magnetizing force superim osed ability than iron when subjected to a variupon a steady magnetizing force, an apable magnetizing force superimposed upon preaching saturation at lower flux densities a steady magnetlzing force of the order of a than iron. few tenths of a gauss. In witness whereof, I. hereunto subscribe 9. A vibrating diaphragm composed of my name this 3rd day of November, A. D. 15 approximately 55% Iron and 45% nickel 1924. heat treated to develop a higher effective permeability than iron when subjected to a GUSTAF W. ELMEN. 

